Cholesterol and cholesterol esters are lipophilic substances which occur in numerous important foodstuffs of animal origin, for example egg yolk, meat, animal fats and the like.
Increased cholesterol values in human blood serum are regarded as being a risk factor for arteriosclerosis and for coronary heart-disease.
By means of a reduction of the intake of cholesterol, in many pathological cases it is possible again to achieve the normal cholesterol values in blood serum. For this reason, the endeavor of the foodstuff industry is to carry out a distinct reduction of the amount of cholesterol and of cholesterol esters in fat-rich foodstuffs of animal origin.
It is thereby an important problem substantially to maintain the sensory and nutrition-physiological properties of the foodstuffs.
Admittedly, a number of processes ere already known fop the separation of cholesterol and cholesterol esters but, because of chemical changes of important components of the starting material, for example of proteins, triglycerides and the like, many of these methods are not suitable for reducing the cholesterol content of foodstuffs.
A relatively gentle process, which has become known only recently, makes use of carbon dioxide high pressure extraction for the removal of cholesterol and of cholesterol esters (cf. V. Krukonis, Supercritical Fluid Processing, International Symposium on Supercritical Fluids, Nice, 1988).
This process is admittedly characterized by the physiological harmlessness of the extraction agent (carbon dioxide) but working at a high pressure is technically rather expensive. Furthermore, under gentle conditions, cholesterol and cholesterol esters cannot be selectively removed therewith because triglycerides are also co-extracted. An improvement of the selectivity by increasing the temperature is admittedly in principle possible but this has a negative effect on the loading of the carbon dioxide with cholesterol and cholesterol esters and on the quality of the product obtained.
From EP-A 0,326,469, it is known to remove cholesterol derivatives from egg yolk with the help of .beta.-cyclodextrin, but in process, the long loading times and the comparatively small reduction of the cholesterol content in the egg yolk is disadvantageous.